<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>Title</title>
</head>
<body>
<form action="checkLessonKey.php" method="post">
    <ul>
        <li><input name="id" type="text" class="id" value="1" onclick="JavaScript:this.value=''"/></li>
        <li><input type="submit" class="loginbtn" value="登录"    />
    </ul>
</form>

</body>
</html>